The 'device-mapper-persistent-data' package provides tools to dump, restore and repair the metadata for thinly provisioned volumes. LVM2 has been enhanced to allow the creation and management of thinly provisioned volumes.

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The 'device-mapper-persistent-data' package provides tools to dump and restore the metadata for thinly provisioned volumes. LVM2 has been enhanced to allow the creation and management of thinly-provisioned volumes.

== Comments and Discussion ==

== Comments and Discussion ==

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Provide the thin provisioning Device Mapper (DM) target and supporting userspace utilities. This DM target allows a single pool of storage to be the backing store of multiple thinly provisioned volumes. Numerous snapshots (and snapshots of snapshots) may be taken of the thinly provisioned volumes.

The main highlight of this implementation, compared to the previous
implementation of snapshots, is that it allows many virtual devices to
be stored on the same data volume. This simplifies administration and
allows the sharing of data between volumes, thus reducing disk usage.

Another significant feature is support for an arbitrary depth of
recursive snapshots (snapshots of snapshots of snapshots ...). The
previous implementation of snapshots did this by chaining together
lookup tables, and so performance was O(depth). This new
implementation uses a single data structure to avoid this degradation
with depth. Fragmentation may still be an issue, however, in some
scenarios.

Metadata is stored on a separate device from data, giving the
administrator some freedom, for example to:

Improve metadata resilience by storing metadata on a mirrored volume but data on a non-mirrored one.

Scalable snapshots of thinly provisioned volumes may be used as the foundation of compelling virtualization and/or cloud services. Fedora would be positioned to be the first distribution to provide this unique advance in Linux block storage.

The bulk of the change is in the kernel (localized to the DM layer) but userspace tools for dumping, restoring and repairing the metadata are also under development. These tools will be provided in a new 'device-mapper-persistent-data' package. In addition the lvm2 package will be updated to ease configuration and management of thin provisioned volumes and their associated snapshots.

A comprehensive test suite has been developed to verify the kernel code works as expected (depends on ruby, dt and dmsetup).

Any additional IO workloads (or benchmarks that model real workloads) that the community has an interest in would be welcomed tests. Data integrity is of utmost importance so all tests that increase confidence in the feature are encouraged.

Users will create a shared pool of storage that will host all thin provisioned volumes and their associated snapshots. So in contrast to the old dm-snapshot implementation the user will not need to manage or monitor the free space of N snapshot volumes -- the storage for thin and snapshot volumes is allocated on-demand from the backing shared pool of storage.

The main highlight of this implementation, compared to the previous
implementation of DM snapshots, is that it allows many virtual devices to
be stored on the same data volume. This simplifies administration and
allows the sharing of data between volumes, thus reducing disk usage.

Another significant feature is support for an arbitrary depth of
recursive snapshots (snapshots of snapshots of snapshots ...). The
previous implementation of snapshots did this by chaining together
lookup tables, and so performance was O(depth). This new
implementation uses a single data structure to avoid this degradation
with depth. Fragmentation may still be an issue, however, in some
scenarios.

Metadata is stored on a separate device from data, giving the
administrator some freedom, for example to:

Improve metadata resilience by storing metadata on a mirrored volume but data on a non-mirrored one.

Improve performance by storing the metadata on SSD.

The 'device-mapper-persistent-data' package provides tools to dump and restore the metadata for thinly provisioned volumes. LVM2 has been enhanced to allow the creation and management of thinly-provisioned volumes.

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